1. Field of the Invention
The present invention relates to a diaphragm assembly for the demand regulator of a breathing apparatus, and particularly to an assembly wherein the diaphragm has varying effective area and also serves as the exhaust valve.
2. Description of the Prior Art
In a typical self-contained underwater breathing apparatus, the regulator includes a first stage that reduces the breathable gas pressure to about 140 psi above ambient, and a second stage that supplies this breathable gas to the diver on demand. Inhalation pressure is sensed by a diaphragm within the second stage that cooperates to open a valve which controls the flow of gas to the diver.
A relatively large area diaphragm is required to sense the slight pressure drop at the beginning of inhalation. However, this large effective area becomes a disadvantage if an aspirator is used. As the flow rate of breathable gas to the diver increases, there is increasing aspiration effect. Thus the pressure drop sensed by the diaphragm increases disproportionately to actual demand. If the aspirator were set for maximum aspiration effect at low flow rates, the diaphragm would be sucked into the regulator case when the flow rate increased. As a result, prior art regulators required that the aspiration effect be minimized at low flow rates. This insured stable operation at higher mass flow rates, but had the disadvantage of reduced aspiration at times of low flow rate, such as at the beginning and end of the inhalation cycle.
An object of the present invention is to provide a demand regulator for a breathing apparatus having a diaphragm of variable effective area that facilitates the use of maximum aspiration at low mass flow rates.
Another shortcoming of prior art regulators is that a separate exhaust valve was provided to permit the escape of exhaled gases. A further object of the present invention is to provide a regulator in which the pressure sensing diaphragm also functions as the exhaust valve.